1PO6-10 The Effect of Magnetic Fields on the Critical Current and Transition Temperatures of Ag-Clad Bi-2223 Tapes
Ben De Mayo, Math/Physics Dept., State Univ. of West Georgia, Carrollton, GA 30118
Presenting Author: B. De Mayo
Magnetic fields were applied to Ag-clad Bi(2223) multifilament, commercially supplied tapes at temperatures from 300K down to 73K. A standard 4-terminal probe method was used to measure the voltage-current properties. Currents of up to 80 A and magnetic fields of up to 300 Gs, perpendicular and parallel to the current flow, were used. The critical current is defined to be the current at which a potential difference per length of 1.0 microV/cm is produced. It was found that perpendicular magnetic fields decreased the critical current linearly up to 300 Gs, where the drop was 50% of the zero field value. Perpendicular magnetic fields also decreased the superconducting transition temperatures linearly up to 300 Gs, where the drop was 5% of the zero field value. Extrapolated to zero, the critical current data imply a critical magnetic field of 560 Gs whereas the transition temperature data extrapolate to a critical magnetic field of 6800 Gs. Parallel magnetic fields had no effect on the critical current or on the transition temperature up to 300 Gs.
1PO6-11 AC Loss Measurement of Bi-2223 Conductors with respect to Applied Time Varying Magnetic Field Direction and Various Matrix Materials
Mi Hae Jang 1, Yong Chu 1, Tae Kuk Ko 1, and SangSoo Oh 2. 1 Department of Electrical Engineering, Yonsei University, Shinchon-dong 134, Seodaemun-gu, Seoul 120-749, Korea. 2 Applied Superconductivity Lab., Head Superconductivity Project Team, Korea Electrotehnology Reserach Institute, P.O. Box 20, Changwon. 641-600, Korea.
Presenting Author: T.K. Ko
In this paper, the AC losses of Bi-2223 tapes with different matrix and different number of superconducting core were measured and analyzed. The three samples produced by a powder-in-tube method are mono-filamentary tape and multi-filamentary tape with Ag matrix, and multi-filamentary tape with Ag-Au matrix.
The measurement was carried out under the environment of constant transport current and applied time-varying magnetic field.
From experiment, losses for fields applied parallel to the c-axis of textured Bi-2223 grains are larger by over an order of magnitude than those applied perpendicular. And it is confirmed that losses for conductor with Ag matrix are larger than those with Ag-Au-Pt matrix.
1PO6-12 AC Loss Analysis of Bi-2223 Tape-Stacked-Cables
Wansoo Nah 1, Junghee Ye 1, Jinho Joo 2, Sang-Soo Oh 3, and Kang-Sik Ryu 3. 1 School of Electrical and Computer Engineering, Sungkyunkwan University, Suwon 440-746, Korea. 2 School of Metallurgical and Materials Engineering, Sungkyunkwan University, Suwon 440-746, Korea. 3 Korea Electrotechnology Research Institute, Changwon 641-120, Korea.
Presenting Author: W. Nah
Practical applications of Bi-2223 tapes to power devices usually require to stack the tapes to be a cable to get large transport current. In this paper, the a.c. loss characteristics of Bi-2223 stacked-cables are analyzed using magnetization method. We measured the magnetization traces of one Bi-2223 tape by using magnetic susceptometer, and those of Bi-2223 stacked-cables by using the typical magnetization method. We stacked the tapes with two different materials; one is with silver paste between the tapes, and the other one with Kapton films. Both mono-filamentary and multi-filamentary tapes were used to get the signals. The hysteresis and coupling losses are estimated from the measured signals, and we discuss the possibility of estimating the a.c. loss characteristics of stacked tapes from the experimental a.c. loss data of one tape.
1PO6-13 Measurements of the a.c. losses in Ag-sheathed PbBi2223 tapes with twisted filaments
T. Hughes 1, J. Horvat 1, F. Darmann 2, and S.X. Dou 1. 1 Institute for Superconducting and Electronic Materials, University of Wollongong, NSW 2522, Australia. 2 Australian Superconductors, P.O. Box 21, Gloucester Boulevard, Port Kembla, NSW 2505, Australia.
Presenting Author: J. Horvat
The total a.c. losses in Bi2223/Ag tapes with twisted and untwisted filaments were measured in applied a.c. magnetic fields. Measurements were made for fields perpendicular and parallel to the face of the tape. The measurements were undertaken using suitable pickup loops and a lock-in amplifier. For the parallel fields the tape with untwisted filaments behaved as if its filaments were fully coupled for all frequencies (37 to 200Hz) and field amplitudes used (<45mT). In this situation, the total losses were accurately described using the Bean model for a 1D slab (assuming the tape acts as a monoblock). In contrast, the losses for the twisted filament tape indicated that the filaments were partially decoupled, and the total losses in this tape were best described by adding the filament hysteresis losses to the coupling current losses. In contrast, in a perpendicular field,the losses for both the twisted and untwisted filament tapes were consistent with fully coupled filaments.
1PO6-14 Enhancement of engineering critical current and homogeneity in km long Bi-2223/Ag-alloy multifilament tapes
Wei G. Wang, Michael D. Bentzon, and P. Vase, Nordic Superconductor Technologies A/S, Priorparken 685, Broendby, DK-2605, Denmark
Presenting Author: W.G. Wang
Long Bi-2223/Ag-alloy multifilament tapes have been produced by the standard powder in tube method. The critical current of the tapes is measured by a contact free method based on measuring remanent fields. This method has a spatial resolution of 2 cm and has been used on km lengths of tape. The defects in the tapes are mainly bubbles and cracks. By eliminating the bubbles and cracks, high engineering critical current tapes of 7 kA/cm2 with homogenous current distribution (standard deviation 2.1 %) and very small thickness variations (standard deviation 1.9 %) have been fabricated in long length.
1PO6-15 Improvement on critical current density of Ag-Mg alloy sheathed Bi-2223 tapes by cryogenic pressing
X.K. Fu, Y.C. Guo, H.K. Liu, and S.X. Dou, Institute for Superconducting and Electronic Materials, University of Wollongong, Wollongong, NSW 2500, Australia
Presenting Author: X.K. Fu
A cryogenic pressing at 77 K, replacing intermediate room temperature pressing between sintering processes, has been applied for fabricating Bi-2223 multi-filamentary tapes The influence of deformation rates of cryogenic pressing on critical current density has been investigated for Ag-sheathed and Ag-Mg alloy sheathed 37 filamentary Bi-2223 tapes. Compared with Ag-sheathed Bi-2223 tapes processed by using same processing procedure, critical currents of Ag-Mg alloy sheathed tapes increase 220%, 260%, 214%, 163%, 95%, 34% at the thickness reduction rate of 8.1%, 11.3%, 12.6%, 15.4%, 19.3% and 21%, respectively. The results reveal that the cryogenic pressing process has significant improvements on critical current density, core mass density, grain alignment and sheath / oxide core interface for Ag-Mg alloy sheathed tapes. The correlation of microstructure, core mass hardness and field dependence of critical current density is discussed in this paper.
1PO6-16 Homogeneity and current transport distribution in Ag-sheathed Bi-2223 multifilamentary tapes
R. Zeng, H.K. Liu, and S.X. Dou, Institute for Superconducting and Electronic Materials, University of Wollongong, NSW 2522, Australia
Presenting Author: R. Zeng
We have investigated homogeneity and current transport distribution in Ag-sheathed Bi-2223 multifilamentary tapes by the magneto-image demonstration and current transport characterisation. It has been indicated that the homogeneity in multifilamentary PIT tapes was strongly depended on the thickness and width of tape or the deformation processing. For thick tape, the higher Jc area was in the centre range and, for the thin tape, the higher Jc area was in edge range at the width direction. Some explanation about the current non-uniform distribution was discussed. The magneto-optical image analysis and current transport distribution measurement illustrated a macro current limited mechanism and provided a method to improve critical current density.
1PO6-17 Magneto-optical investigations of multifilamentary Bi-2223 tapes
Michael R. Koblischka 1, T.H. Johansen 2, B. Larsen 3, N.H. Andersen 3, H. Wu 1, P. Skov-Hansen 1, M. Bentzon 1, and P. Vase 1. 1 Nordic Superconductor Technologies, Priorparken 685, DK-2605 Broendby, Denmark. 2 University of Oslo, Department of Physics, N-0316 Oslo, Norway. 3 Risoe National Laboratory, Condensed Matter Physics and Chemistry Department, DK-4000 Roskilde, Denmark.
Presenting Author: M.R. Koblischka
Flux distributions of multifilamentary Bi-2223 tapes with a varying number of filaments (14 to 55 filaments) are investigated by magneto-optic (MO) imaging at various temperatures (10 K < T < 77 K) and in different orientations (field Ha applied perpendicular to the tape surface and perpendicular to a cross section of the tape). This enables to study differences between the individual filaments in a direct way. The importance of granularity and structural defects is analyzed using a field-reduction procedure, which allows to detect weaker superconducting regions. Furthermore, from an analysis of the field distributions of the intact cross sections we obtain important informations concerning the filament quality as a function of position, and the filament coupling.
1PO6-18 Thermal conductivity of Bi(2223) tapes with different metallic sheaths
Marina Putti 1, Carlo Ferdeghini 1, Gianni Grasso 1, Andrea Manca 1, and Wilfried Goldacker 2. 1 INFM, Dipartimento di Fisica, Universita` di Genova, Via Dodecaneso 33, 16146, Genova. 2 Forschungszentrum Karlsruhe, ITP, P.O. Box 3640, 76021 Karlsruhe, Germany.
Presenting Author: M. Putti
To improve mechanical and thermal properties, different Ag alloys are employed for fabrication of Bi(2223) superconducting tapes by Power-in-Tube technique. Mechanical strength and resistivity are the typical characterization performed on these materials; thermal conductivity is not in general measured. Therefore, information on thermal properties, are obtained from literature data or derived from resistivity measurements through the Wiedeman-Franz Law (WFL). Both these approaches are not correct for mainly two reasons, thermal conductivity is strongly sample and preparation dependent, and in alloys the phonon contribution to the heat conduction may become important.
We have measured resistivity and thermal conductivity of several tapes with different sheaths: pure Ag, AgAu and AgMg. These last have been manufactured without superconducting core with the aim of determining the best heat treatment conditions for reaching low thermal conductivity, high electrical resitivity and mechanical strength. We find that the both AgAu and AgMg alloys show very low residual resitivity ratios (RRR=2.3-1.3). The thermal conductivity results are quite surprising. In fact, despite of the alloys resistivities being nearly the same, the thermal conductivity of AgMg alloys is more than three times lower than those of AgAu ones. This result may be understood taking into account the phonon contribution to the thermal conductivity. At low temperature, the latter is limited by the grain boundaries, and owing to the tendency of Mg to precipitate partly at the grain boundaries, the dimension of grains in AgMg alloys occur to be 10 times lower (2-3 microns) than in AgAu alloys. Therefore, these results confirm that the metallic sheath can be successfully modified for the purpose of reducing its thermal conductivity.
1PO6-19 Stress Effects for Bi-Based Superconducting Tapes
Zhengdao Wang, Cryogenic Laboratory, Chinese Academy of Science, Beijing 100080 and Zhaojia Chen, Institute of Physics, Chinese Academy of Science, Beijing 100080
Presenting Author: Z. Chen
The mechanical properties of Bi2223 multistrand superconducting tapes are very important in pratical application. In this paper, we design a new tensile device, which can simultaneously measure parameters of mechanical and electrical in magnetic field. By it, we research the relationship of the critical current versus stress, strain and magnetic field. The irreversible stress and strain for some superconducting tapes and the relaxation phenomena have been given.